Conventionally, many organic fluorescent substances are used as a material for a fluorescent pigment. The fluorescent pigment can be produced by incorporating a fluorescent substance into a resin by kneading at a temperature not lower than the softening temperature of the resin.
A fluorescent pigment obtained by powdering a solid solution of a fluorescent substance soluble in an organic solvent and a synthetic resin is also known. Such a fluorescent pigment is obtained by kneading a fluorescent substance with a synthetic resin at a temperature not lower than a softening temperature of the synthetic resin using a kneader and by finely pulverizing after cooling. The resulted fluorescent pigment powder can be incorporated into a further resin by kneading at a temperature not lower than the softening temperature of the further resin to produce a fluorescent resin.
However, a conventional organic fluorescent pigment uses an organic compound having a low molecular weight as a fluorescent substance. When such a fluorescent pigment is kneaded into a resin to obtain a fluorescent resin, the bleeding phenomenon in which the fluorescent substance migrates to the surface of the resin with time tends to occur. In a fluorescent resin in which the bleeding phenomenon has occurred, there is a problem that a fluorescent substance is easily desorbed and the fluorescence intensity of the fluorescent resin decreases with time. A fluorescent substance which has migrated to the surface of a fluorescent resin may be transferred to an object which contacts with the fluorescent resin, and color transfer occurs.
Patent Document 1 describes a process for reducing the bleeding phenomenon in which a fluorescent pigment having not a low molecular weight but a high molecular weight is synthesized and the resulted fluorescent pigment having a high molecular weight is kneaded into a resin. However, such a process is also the incorporation into the resin. Accordingly, a possibility that a bleeding phenomenon occurs still remains. In addition, such a process requires two steps of synthesizing a fluorescent pigment having a high molecular weight; and kneading with a resin to obtain a fluorescent resin.
Therefore, the development of a fluorescent resin which itself has fluorescence and does not cause a bleeding phenomenon is required.
A liquid crystal polymer is excellent in mechanical properties, moldability, chemical resistance, gas barrier properties, moisture resistance, electrical properties, etc. Accordingly, a liquid crystal polymer is used for components in various fields. Particularly, a liquid crystal polymer is excellent in heat resistance and thin-wall formability. Accordingly, the use of a liquid crystal polymer is expanding to electronic components such as precision instruments.
On the other hand, it is known in a molded article composed of a liquid crystal polymer that the surface of a resin is peeled off by ultrasonic cleaning or sliding with other members and the fuzzy phenomenon occurs. Hereinafter, the fuzzy phenomenon will be referred to as “fibrillation”. In a precision instrument, especially an optical instrument with a lens, slight dust and dirty affect performance of the instrument. When small dust, oil, dirty and the like adhere to a lens in a component used for an optical instrument such as a camera module, the optical characteristics of the camera module is remarkably deteriorated.
In order to prevent such deterioration of the optical characteristics, a component constituting the camera module is usually subjected to the ultrasonic cleaning prior to assembly, and small dust, dirty and the like adhering to the surface are removed.
However, powder generated by the fibrillation on the surface of a molded article composed of a liquid crystal polymer in the ultrasonic cleaning as described above becomes foreign matter when assembling the camera module and when using the camera. As a result, there is a problem that the optical characteristics of a camera module are remarkably deteriorated.
As a process for suppressing the fibrillation, it is known to add an inorganic particle such as hydrophobic silica to a resin. However, there is a problem that an inorganic particle such as silica has a weak absorptivity with a resin and bleeds out. A fine particle bled out may be a foreign substance which deteriorates the optical characteristics of the camera module even if the fine particle is extremely minute and the amount thereof is very small.
Further, a liquid crystal polyester resin composition which suppresses the fibrillation by containing barium sulfate having a particle diameter of 1 μm or less is proposed (Patent Document 2). However, the resin composition contains barium sulfate in a large amount of 5 to 40 parts by volume. Also, the problem that barium sulfate bleeds out cannot be avoided.
Accordingly, there has been a need for a liquid crystal polymer which has an effect of suppressing the fibrillation and does not contain any substance which bleeds out.
Patent Document 1: JP-A-2004-250536
Patent Document 2: JP-B-5695389